How can I preserve texture details when viewed from a distance?
It seems that Cycles does not allow to disable texture filtering as of now.

My solution is to render the scene at an insane resolution, but also to reduce the sample count by the same factor, and then downsample the result. It works very well this way.

If I haven't overlook something, I think, this is an urgently missing feature. It basically makes all textures look a little bit blurry if rendered directly at the intended resolution (because mipmapping is visually inferior to supersampling—especially for bump maps).